FLOOD06195

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Measurment of Peak Discharge at Culverts by Indirect Methods
• Date: 6/1/1968
• Prepared By: G.L. Bodhaine
• Floodplain - Doc Type: Educational/Technical/Reference Information

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TECHNIQUES OF WATER-RESOURCES lNVESTIGATIONS

10

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'" Critical-flow section
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de

-1-

Q =a constant

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TranQuil flow and mild slopes

1
Rapid flow and steep Slopes

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2

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SPECIFIC ENERGY (Ho = d +

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V 2
-" I. IN FEET
29

10

12

Figure 3.-Relation betwe1i!" specific energy and depth.

For the condition of minimum specific energy
and critical depth, the discharge equation for a
section of any shape can be written

d,=maximum depth of water in the eriti-
cal-flo"\I~ section, and
D=inside diameter of circular section,

Q=A:"#

(1)

The two types of flow in this classification are
1 and 2,

or

Type 1 flow

In type 1 flow, as illustrated on figure 2, the
water passes through critical depth near the
culvert entrance. The headwater-diameter ratio,
(h,-z)/D, is limited to a maximum of 1.5 and
the culvert barrel flows partly full. The slope
of the culvert barrel, So> must be greater than
the critical slope, S" and the tailwater elevation,
h" must be less than the elevation of the water
surface at the control section, h.,
The discharge equation is

Q=CA,.J29 (h,-z+ "I;' ~ -~,-h~l:~} (5)
g

Q=A,{!j(l;"

(2)

The discharge equation can be simplified
according to the shape of the sections. Thus,
for rectangular sections,

Q=5.67bd:I',

(3)

and for circular sections,

Q=C,D'I',

(4)

where

b=width of section,
C,=function of d,/D,

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